How do zinc oxide and zero valent iron nanoparticles impact the occurrence of antibiotic resistance genes in landfill leachate?

Abstract

Landfill leachate has been identified as a significant reservoir of antibiotic resistance genes (ARGs). Metallic nanoparticles (M-NPs) increasingly incorporated into various consumer products are eventually disposed in landfills and leached into leachate. However, little is known about the impact of M-NPs on the occurrence of ARGs in leachate. Here, we investigated the changes of ARGs for 56 days in leachate exposed to different concentrations of two representative M-NPs, i.e. zinc oxide (ZnO) and zero valent iron (Fe⁰) NPs. The results showed that ZnO NP exposure increased ARG abundances, and Fe⁰ NP exposure decreased ARG abundances. Most of the ARG abundances were significantly associated with mobile genetic elements (MGEs). Furthermore, the presence of ZnO and Fe⁰ NPs induced obvious changes in bacterial community. Network analysis revealed significant bacteria-ARG co-occurrence patterns, indicating that the shifted bacterial community was an important factor explaining the changed ARG patterns. Structural equation models suggested that ZnO NP exposure increased the abundances of ARGs by dominantly driving changes in bacterial community, followed by the increase in MGEs, whereas the decreased abundances of ARGs were mainly associated with the reduction of MGEs mediated by Fe⁰ NPs. These findings can provide a theoretical reference for future evaluation of public health risks of M-NPs and promote the mechanistic understanding of M-NP-induced ARG dissemination or attenuation in the environment.